These AR15 anti walk / anti rotation hammer and trigger pins are what you need to keep your receiver from excessive wear and tear. Keeping the hammer and trigger pins from rotating is especially important when shooting full auto or with pistol caliber builds, such as 9mm AR15's.
Strike Industries Anti-Walk Trigger, Hammer Pin Kit AR-15 Steel Matte
RISE Armament Anti-Walk Trigger and Hammer Pins
Armaspec Anti-Walk Trigger / Hammer Pins Stainless .154 for ar-15 lower (CT35ARMASPEC136SS)
Rise Armament Anti-Walk Hammer, Trigger Pins AR-15
AR-15 Complete Anti-Rotation Trigger/Hammer Pin Set (Anodized Clear) » Guntec USA
KNS AR-15/ AR-10 Gen 2 Mod 2 Stainless Steel Barbell-Style Anti-Walk Trigger /
Armaspec Anti-Walk Trigger / Hammer Pins Stainless .154 for ar-15 lower (CT35ARMASPEC136SS)
MMC Combos AR 15 Trigger Upgrade Kit Including Davidson SKU: CO-82421
Titanium AR Anti-Walk Hammer & Trigger Pin Set
Trigger Upgrade Kit Trigger + LPK + Grip + Anti Walk Pins
Strike Industries Anti-walk/Anti-rotation Trigger/Hammer Pins
AR Platform Anti-Walk Pins - Stailess Steel